1. Technical Field
The present invention relates to an external air introduction apparatus that opens and closes an external air introduction opening that guides external air into exhaust gas.
2. Related Art
In recent years, exhaust gas regulations have been tightened not only regarding the automotive engines but also regarding general-purpose engines used in construction machines, agricultural machines, etc. Therefore, configurations in which a catalyst is provided in an exhaust muffler to burn unburned fuel gas remaining in exhaust gas, as in a general-purpose engine described in Japanese Unexamined Patent Application Publication No. 2005-83254, have been proposed. Such an exhaust muffler adopts a configuration that includes an external air introduction opening that introduces external air so that external air mixes with exhaust gas to increase the oxygen concentration and promote combustion of unearned fuel gas.